Keira Knightley clashed with Atonement director Joe Wright because they could not agree on which character she should play.

The actress refused to play the part of Briony in the adaptation of Ian McEwan's novel because she wanted to take on the more challenging role of Cecilia.

"Joe thought I should play the middle Briony but I read the script and instantly liked Cecilia. I loved her acerbic quality. I have never done that - she is hiding so much," Knightley told Empire magazine.

"So we had this big long talk where I was arguing for Briony. We finally decided on Cecilia because she has none of that Elizabeth Bennet vibe."